1. Field of the Invention
The present invention relates to a newly constructed on-line moisture control method wherein powdered or granular materials including inorganic materials such as resin and ceramic are automatically sampled and the moisture content thereof quickly measured and to an on-line moisture control system for performing the method.
2. Prior Art
Generally, keeping the moisture content of resin materials constant in order to maintain good quality of the resin products has created a most important problem because with an inappropriate moisture content of the resin materials to be supplied into a molding machine defects such as a silver line or void are caused. Therefore, resin materials are usually dried by the use of a hopper dryer prior to being supplied into the molding machine.
However, before the resin materials are fed into the hopper dryer, they are apt to absorb moisture in the air while stored in a silo or a tank of intermediate stage for a fixed period of time after a kraft bag or a flexible container which is used to carry resin materials is opened. Accordingly a fixed heating temperature and a fixed heating time are set for the hopper dryer, which is based on an estimated moisture content of the resin materials. But such a conventional method for drying resin materials by the use of a hopper dryer leaves further room for improvement in saving labor.
On the other hand, a titration analysis using a Karl Fischer reagent has been conventionally known as a method for analyzing and measuring the moisture content of resin materials. A moisture measuring unit has been developed in which a titration analysis by a Karl Fischer reagent is performed by means of a coulometric method, a volumetric method and an absorptive photometric method, whereby a high accuracy can be obtained.
FIGS. 8 and 9 show the basic construction of a coulometric moisture measuring unit.
This unit is constructed such that a moisture measuring analyzer 61 which performs a coulometric titration by means of a Karl Fischer reagent is connected to a heating chamber 63 to heat samples such as powdered or granular materials. In the chamber 63 connected with the analyzer 61 through a conduit 62, powdered or granular materials 66 put on a boat 65 are transferred and contained by an automatic sample loading unit 67. The moisture produced by heating the materials 66 in the chamber 63 is introduced into the analyzer 61 together with a nitrogen gas fed into the chamber 63, the moisture being titrated and analyzed by a Karl Fischer reagent by the use of coulometric titration. Then the result of the analysis is shown on a display 70.
However, such a moisture analyzer 61 has troublesome problems because the following procedures must be repeated for each sample of the materials.
In order to feed sample materials 66 into the heating chamber 63, the boat 65 is inserted by opening an insert port 64a of an insertion pipe 64 extending from the heating chamber 63 by reducing the caliber and is pushed into a sample feeding portion 64b by means of a rod 65a, the materials 66 sampled by a sampling unit (not illustrated) being loaded on the boat 65 thus contained in the pipe 64 after a cap 64c of the feeding portion 64b is removed.
In this case, a feeding machine (not illustrated) which contains sample materials 66 is mated with the cap 64c so that the opening of the feeding machine fits the opening of the cap 64c. After a purge valve 69 is opened to atmosphere, a dried pressurized nitrogen gas supplied through a feed pipe 68b and a drying chamber 68a from a gas cylinder 68 is replaced and discharged in order to prevent outside air from entering into the heating chamber 63.
Further, after completion of the heat treatment, the materials 66 loaded on the boat 65 are transferred by the automatic loading unit 67 into the insert port 64a of the insertion pipe 64 to be discharged.
According to the above-mentioned troublesome problems, as a rule, such a moisture measuring analyzer has been used for quality inspection at a laboratory by a professional inspector. It is hardly possible to sample powdered or granular materials one after another and measure the moisture content thereof at a molding site.